Antibiotic Targets

Introduction to Antibiotics

  • Antibiotics are drugs designed to target bacteria and inhibit their growth or kill them.

  • Drug Target Definition: A specific site on the bacterial cell that antibiotics can target to destroy or prevent the growth of bacteria.

  • Selective Toxicity: The concept of selectively targeting bacterial cells while minimizing harm to human cells.

Major Classes of Antibiotics

  • There are five major classes of antibiotics based on their targets within bacterial cells.

    • Cell wall inhibitors, cell membrane, DNA/RNA, protein synthesis inhibitors acting on ribosomes, and metabolic pathways and products.

  • Important Note: Antibiotics are only effective against actively growing bacteria and do not work on dormant bacteria or endospores.

1. Cell Wall Inhibitors

The most important class od drug.

  • Definition: A class of antibiotics that target and destroy peptidoglycan, a unique component of bacterial cell walls.

  • Importance: Peptidoglycan is an ideal target for selective toxicity since it is found only in bacteria, not humans.

  • Mechanism of Action: These drugs disrupt the structural integrity of the bacterial cell wall, causing the bacteria to become leaky and eventually leading to cell lysis and death.

Key Drugs in this Class:

  • Penicillins

    • Major group of cell wall inhibitors.

  • Cephalosporins

    • Similar action to penicillins; effective in destroying peptidoglycan.

    • Examples: Keflex.

    • Drugs in this category often start with "-kef, -ceph, and -cef."

  • Bacitracin

    • A topical treatment, it is very toxic and cannot be taken orally, specifically effective on Gram-positive bacteria.

  • Vancomycin

    • A drug of last resort used for severe infections like MRSA (Methicillin-resistant Staphylococcus aureus).

    • Administered intravenously only.

  • Isoniazide

    • Targeted against acid-fast bacteria, such as Mycobacterium tuberculosis.

    • Works by disrupting the protective waxy layer of these bacteria.

2. Cell Membrane Inhibitors

Cell membrane target drugs are poorly selective because humans and bacteria have a cell membrane.

  • Definition: Antibiotics that target bacterial cell membranes.

  • Selectivity Challenge: Both bacteria and humans have cell membranes, making it hard to achieve selective toxicity.

Key Drug:

  • Polymyxin

    • A narrow-spectrum antibiotic that primarily targets Gram-negative bacteria.

    • Mechanism of action: Inserts into the membrane, creating gaps that lead to leakage of cellular contents, resulting in cell death.

3. DNA and RNA Synthesis Inhibitors

DNA/RNA target drugs are poorly selective because humans and bacteria have DNA/RNA.

  • Definition: Antibiotics that target enzymes involved in bacterial DNA replication or RNA production.

  • Selectivity Challenge: Humans also possess DNA and RNA, so these drugs must selectively target bacterial-specific enzymes.

Key Drug:

  • Quinolones

    • Example: Cipro (Ciprofloxacin).

    • Commonly prescribed for urinary tract infections and other types of infections by inhibiting DNA replication enzymes.

4. Protein Synthesis Inhibitors Acting on Ribosomes

  • Definition: Drugs that inhibit bacterial ribosomes' functions, which are essential for protein synthesis.

  • Selectivity: Bacterial ribosomes differ in size and structure from human ribosomes (30S and 50S subunits).

Key Drugs in this Class:

  • Tetracycline

    • Targets the 30S ribosomal subunit.

  • Aminoglycosides

    • Examples: Gentamicin, Streptomycin.

    • Commonly used antibiotics in clinical settings.

  • Clindamycin

    • Targets the 50S subunit; often used to treat acne.

  • Erythromycin

    • Commonly prescribed for eye infections.

  • Chloramphenicol

    • An exceptionally toxic drug used only in severe cases due to potential side effects.

5. Metabolic Pathways and Products

  • Definition: Antibiotics that inhibit specific metabolic pathways essential for bacterial growth and survival.

    • Inhibits the bacteria from making specific products they need.

  • Selectivity: These drugs can target metabolic pathways unique to bacteria and not humans.

Key Drugs in this Class:

  • Sulfa Drugs

    • Examples: Sulfonamide, Trimethoprim.

    • Function by inhibiting specific bacterial metabolic pathways, such as those required for folic acid synthesis.